Patellar alignment compared between kinematic and mechanical unicompartmental knee arthroplasties

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Radiology

Background:

• Unicompartmental knee arthritis is commonly treated with unicompartmental knee arthroplasty (UKA).
• UKA can be performed using traditional mechanical alignment or kinematic alignment techniques.
• Patellar tendon alignment is a critical factor in knee function post-arthroplasty.

Purpose of the Study:

• To compare pre- and post-operative patellar tendon alignment between mechanical and kinematic UKA.
• To evaluate the accuracy of sagittal patella-femoral alignment using Insall-Salvati and Blackburne-Peel ratios.
• To assess the variability in alignment outcomes between the two surgical techniques.

Main Methods:

• Retrospective study of 156 partial knee arthroplasties (95 mechanical, 61 kinematic) from 2015-2022.
• Evaluation of pre- and post-operative Insall-Salvati and Blackburne-Peel ratios.
• Analysis of X-ray imaging by a blinded, musculoskeletal-trained radiologist.

Main Results:

• Kinematic UKA demonstrated improved accuracy in reproducing Insall-Salvati and Blackburne-Peel ratios compared to mechanical UKA.
• Statistically significant differences were found in operative Insall-Salvati ratios between kinematic and mechanical groups.
• Kinematically aligned knees showed a highly significant difference between postoperative Blackburne-Peel and Insall-Salvati ratios (p < 2.33 x 10^-16).
• A significant difference in the standard deviation of the Blackburne-Peel ratio difference was noted between mechanical and kinematic groups (p=0.00183).

Conclusions:

• Kinematic alignment more accurately reproduces sagittal patella-femoral knee alignment in UKA.
• Greater variability in alignment outcomes was observed within the kinematically aligned cohort.
• These findings suggest kinematic alignment may offer advantages in restoring natural patellar tracking.